This invention relates generally to transaxles and, more particularly, relates to an integrated hydrostatic transaxle comprising a controlled traction differential.
As is known, the use of a standard differential assembly in the transmission system of a motor vehicle allows the wheels to spin at different speeds. In the case of a vehicle traveling in a straight line, the axle shafts connected to the standard differential assembly will rotate at the same speed. However, when a turn or curve is encountered, the axle shaft nearest the inside of the turn will slow in rotational speed while the outer axle shaft will simultaneously increase in rotational speed. As such, the wheels, driven by the axle shafts, are prevented from scuffing the surface across which they travel.
While the standard differential assembly serves an important function in the operation of a transmission system, the standard differential of simple construction has difficulty operating under certain conditions. For example, when a first one of the drive tires is disposed in wet, muddy, or loose soil conditions, or when the first drive tire has been partially or completely removed from contact with the ground, the coefficient of friction under the first drive tire will be substantially lower than that associated with the second drive tire. This resulting frictional imbalance will tend to cause the second drive tire to remain stationary while the first drive tire will spin without moving the vehicle.
To solve the problem of loss of traction in larger transaxle systems, a variety of techniques has been developed to reduce the tendency of the transaxle to differential. For example, U.S. Pat. No. 3,528,323 to Kamlukin, issued Sep. 15, 1970, discloses a means for preventing free spinning of one of the driven shafts of a transaxle without interfering with the normal differential capability of the transaxle. In particular, the '323 patent discloses the use of a coil spring to outwardly force the gears of the differential into engagement with the differential housing thereby introducing a frictional force into the assembly which acts to resist relative rotation of the axle shafts. In this manner, the frictional force limits the free spinning of one axle shaft while the other remains stationary.
While the friction inducing means disclosed in the '323 patent works for its intended purpose to provide larger transaxles with a controlled traction differential assembly, the use of coil springs to apply the frictional force often requires special tools and/or procedures for use in applying the forces necessary to set the springs. These additional tools and/or procedures undesirably results in increased manufacturing costs. Therefore, there remains a need for a controlled traction differential assembly which is simpler to construct, can be produced at a lower cost, and which can be readily incorporated into a smaller transaxle such as an integrated hydrostatic transaxle.
As a result of these existing needs, it is an object of the present invention to provide an integrated hydrostatic transaxle having a controlled traction differential assembly which will provide the hydrostatic transaxle with the benefits and advantages which have accrued to other types of transaxles that use controlled traction differential assemblies.
It is a further object of the present invention to provide a controlled traction differential assembly which is cost effective and relatively easy to manufacture.
It is still a further object of the present invention to provide a controlled traction cartridge for use in conveniently converting a standard differential assembly into a controlled traction differential assembly.
It is yet a further object of the present invention to provide a controlled traction differential assembly in which the breakdown bias, i.e., the amount of torque required to cause the differential to operate, may be easily varied.